WARSAW, Poland -- Polish police said they have arrested seven people and seized about 500,000 marijuana plants in a raid of hidden plantations in northwestern Poland.

An anti-narcotics police team arrested two people and confiscated 800 marijuana plants when they uncovered a specially equipped underground marijuana plantation in a village near Szczecin, the Polish news.pl Web site said Friday.

This was the fourth closure of a marijuana plantation in the Szczecin region this year, police said.

The plantation was located in a potato cellar, equipped with irrigation and ventilation systems and with artificial lighting.